<!DOCTYPE html><html><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1"><style>@font-face {
font-family: octicons-link;
src: url(data:font/woff;charset=utf-8;base64,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) format('woff');
}
@media (prefers-color-scheme: dark) {
body,
[data-theme="dark"] {
/*dark*/
color-scheme: dark;
--color-prettylights-syntax-comment: #8b949e;
--color-prettylights-syntax-constant: #79c0ff;
--color-prettylights-syntax-entity: #d2a8ff;
--color-prettylights-syntax-storage-modifier-import: #c9d1d9;
--color-prettylights-syntax-entity-tag: #7ee787;
--color-prettylights-syntax-keyword: #ff7b72;
--color-prettylights-syntax-string: #a5d6ff;
--color-prettylights-syntax-variable: #ffa657;
--color-prettylights-syntax-brackethighlighter-unmatched: #f85149;
--color-prettylights-syntax-invalid-illegal-text: #f0f6fc;
--color-prettylights-syntax-invalid-illegal-bg: #8e1519;
--color-prettylights-syntax-carriage-return-text: #f0f6fc;
--color-prettylights-syntax-carriage-return-bg: #b62324;
--color-prettylights-syntax-string-regexp: #7ee787;
--color-prettylights-syntax-markup-list: #f2cc60;
--color-prettylights-syntax-markup-heading: #1f6feb;
--color-prettylights-syntax-markup-italic: #c9d1d9;
--color-prettylights-syntax-markup-bold: #c9d1d9;
--color-prettylights-syntax-markup-deleted-text: #ffdcd7;
--color-prettylights-syntax-markup-deleted-bg: #67060c;
--color-prettylights-syntax-markup-inserted-text: #aff5b4;
--color-prettylights-syntax-markup-inserted-bg: #033a16;
--color-prettylights-syntax-markup-changed-text: #ffdfb6;
--color-prettylights-syntax-markup-changed-bg: #5a1e02;
--color-prettylights-syntax-markup-ignored-text: #c9d1d9;
--color-prettylights-syntax-markup-ignored-bg: #1158c7;
--color-prettylights-syntax-meta-diff-range: #d2a8ff;
--color-prettylights-syntax-brackethighlighter-angle: #8b949e;
--color-prettylights-syntax-sublimelinter-gutter-mark: #484f58;
--color-prettylights-syntax-constant-other-reference-link: #a5d6ff;
--color-fg-default: #e6edf3;
--color-fg-muted: #848d97;
--color-fg-subtle: #6e7681;
--color-canvas-default: #0d1117;
--color-canvas-subtle: #161b22;
--color-border-default: #30363d;
--color-border-muted: #21262d;
--color-neutral-muted: rgba(110,118,129,0.4);
--color-accent-fg: #2f81f7;
--color-accent-emphasis: #1f6feb;
--color-success-fg: #3fb950;
--color-success-emphasis: #238636;
--color-attention-fg: #d29922;
--color-attention-emphasis: #9e6a03;
--color-attention-subtle: rgba(187,128,9,0.15);
--color-danger-fg: #f85149;
--color-danger-emphasis: #da3633;
--color-done-fg: #a371f7;
--color-done-emphasis: #8957e5;
}
}
@media (prefers-color-scheme: light) {
body,
[data-theme="light"] {
/*light*/
color-scheme: light;
--color-prettylights-syntax-comment: #57606a;
--color-prettylights-syntax-constant: #0550ae;
--color-prettylights-syntax-entity: #6639ba;
--color-prettylights-syntax-storage-modifier-import: #24292f;
--color-prettylights-syntax-entity-tag: #116329;
--color-prettylights-syntax-keyword: #cf222e;
--color-prettylights-syntax-string: #0a3069;
--color-prettylights-syntax-variable: #953800;
--color-prettylights-syntax-brackethighlighter-unmatched: #82071e;
--color-prettylights-syntax-invalid-illegal-text: #f6f8fa;
--color-prettylights-syntax-invalid-illegal-bg: #82071e;
--color-prettylights-syntax-carriage-return-text: #f6f8fa;
--color-prettylights-syntax-carriage-return-bg: #cf222e;
--color-prettylights-syntax-string-regexp: #116329;
--color-prettylights-syntax-markup-list: #3b2300;
--color-prettylights-syntax-markup-heading: #0550ae;
--color-prettylights-syntax-markup-italic: #24292f;
--color-prettylights-syntax-markup-bold: #24292f;
--color-prettylights-syntax-markup-deleted-text: #82071e;
--color-prettylights-syntax-markup-deleted-bg: #ffebe9;
--color-prettylights-syntax-markup-inserted-text: #116329;
--color-prettylights-syntax-markup-inserted-bg: #dafbe1;
--color-prettylights-syntax-markup-changed-text: #953800;
--color-prettylights-syntax-markup-changed-bg: #ffd8b5;
--color-prettylights-syntax-markup-ignored-text: #eaeef2;
--color-prettylights-syntax-markup-ignored-bg: #0550ae;
--color-prettylights-syntax-meta-diff-range: #8250df;
--color-prettylights-syntax-brackethighlighter-angle: #57606a;
--color-prettylights-syntax-sublimelinter-gutter-mark: #8c959f;
--color-prettylights-syntax-constant-other-reference-link: #0a3069;
--color-fg-default: #1F2328;
--color-fg-muted: #656d76;
--color-fg-subtle: #6e7781;
--color-canvas-default: #ffffff;
--color-canvas-subtle: #f6f8fa;
--color-border-default: #d0d7de;
--color-border-muted: hsla(210,18%,87%,1);
--color-neutral-muted: rgba(175,184,193,0.2);
--color-accent-fg: #0969da;
--color-accent-emphasis: #0969da;
--color-success-fg: #1a7f37;
--color-success-emphasis: #1f883d;
--color-attention-fg: #9a6700;
--color-attention-emphasis: #9a6700;
--color-attention-subtle: #fff8c5;
--color-danger-fg: #d1242f;
--color-danger-emphasis: #cf222e;
--color-done-fg: #8250df;
--color-done-emphasis: #8250df;
}
}
body {
max-width: 980px;
margin: 16px auto;
background-color: var(--color-canvas-default);
}
.markdown-body .octicon-link:before {
font: normal normal normal 16px/1 octicons-link;
display: inline-block;
text-decoration: none;
text-rendering: auto;
-webkit-font-smoothing: antialiased;
-moz-osx-font-smoothing: grayscale;
-webkit-user-select: none;
-moz-user-select: none;
-ms-user-select: none;
user-select: none;
content: '\f05c';
vertical-align: middle;
}
.markdown-body {
-ms-text-size-adjust: 100%;
-webkit-text-size-adjust: 100%;
margin: 0;
color: var(--color-fg-default);
background-color: var(--color-canvas-default);
font-family: -apple-system,BlinkMacSystemFont,"Segoe UI","Noto Sans",Helvetica,Arial,sans-serif,"Apple Color Emoji","Segoe UI Emoji";
font-size: 16px;
line-height: 1.5;
word-wrap: break-word;
}
.markdown-body .octicon {
display: inline-block;
fill: currentColor;
vertical-align: text-bottom;
}
.markdown-body h1:hover .anchor .octicon-link:before,
.markdown-body h2:hover .anchor .octicon-link:before,
.markdown-body h3:hover .anchor .octicon-link:before,
.markdown-body h4:hover .anchor .octicon-link:before,
.markdown-body h5:hover .anchor .octicon-link:before,
.markdown-body h6:hover .anchor .octicon-link:before {
width: 16px;
height: 16px;
content: ' ';
display: inline-block;
background-color: currentColor;
-webkit-mask-image: url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 16 16' version='1.1' aria-hidden='true'><path fill-rule='evenodd' d='M7.775 3.275a.75.75 0 001.06 1.06l1.25-1.25a2 2 0 112.83 2.83l-2.5 2.5a2 2 0 01-2.83 0 .75.75 0 00-1.06 1.06 3.5 3.5 0 004.95 0l2.5-2.5a3.5 3.5 0 00-4.95-4.95l-1.25 1.25zm-4.69 9.64a2 2 0 010-2.83l2.5-2.5a2 2 0 012.83 0 .75.75 0 001.06-1.06 3.5 3.5 0 00-4.95 0l-2.5 2.5a3.5 3.5 0 004.95 4.95l1.25-1.25a.75.75 0 00-1.06-1.06l-1.25 1.25a2 2 0 01-2.83 0z'></path></svg>");
mask-image: url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 16 16' version='1.1' aria-hidden='true'><path fill-rule='evenodd' d='M7.775 3.275a.75.75 0 001.06 1.06l1.25-1.25a2 2 0 112.83 2.83l-2.5 2.5a2 2 0 01-2.83 0 .75.75 0 00-1.06 1.06 3.5 3.5 0 004.95 0l2.5-2.5a3.5 3.5 0 00-4.95-4.95l-1.25 1.25zm-4.69 9.64a2 2 0 010-2.83l2.5-2.5a2 2 0 012.83 0 .75.75 0 001.06-1.06 3.5 3.5 0 00-4.95 0l-2.5 2.5a3.5 3.5 0 004.95 4.95l1.25-1.25a.75.75 0 00-1.06-1.06l-1.25 1.25a2 2 0 01-2.83 0z'></path></svg>");
}
.markdown-body details,
.markdown-body figcaption,
.markdown-body figure {
display: block;
}
.markdown-body summary {
display: list-item;
}
.markdown-body [hidden] {
display: none !important;
}
.markdown-body a {
background-color: transparent;
color: var(--color-accent-fg);
text-decoration: none;
}
.markdown-body abbr[title] {
border-bottom: none;
-webkit-text-decoration: underline dotted;
text-decoration: underline dotted;
}
.markdown-body b,
.markdown-body strong {
font-weight: var(--base-text-weight-semibold, 600);
}
.markdown-body dfn {
font-style: italic;
}
.markdown-body h1 {
margin: .67em 0;
font-weight: var(--base-text-weight-semibold, 600);
padding-bottom: .3em;
font-size: 2em;
border-bottom: 1px solid var(--color-border-muted);
}
.markdown-body mark {
background-color: var(--color-attention-subtle);
color: var(--color-fg-default);
}
.markdown-body small {
font-size: 90%;
}
.markdown-body sub,
.markdown-body sup {
font-size: 75%;
line-height: 0;
position: relative;
vertical-align: baseline;
}
.markdown-body sub {
bottom: -0.25em;
}
.markdown-body sup {
top: -0.5em;
}
.markdown-body img {
border-style: none;
max-width: 100%;
box-sizing: content-box;
background-color: var(--color-canvas-default);
}
.markdown-body code,
.markdown-body kbd,
.markdown-body pre,
.markdown-body samp {
font-family: monospace;
font-size: 1em;
}
.markdown-body figure {
margin: 1em 40px;
}
.markdown-body hr {
box-sizing: content-box;
overflow: hidden;
background: transparent;
border-bottom: 1px solid var(--color-border-muted);
height: .25em;
padding: 0;
margin: 24px 0;
background-color: var(--color-border-default);
border: 0;
}
.markdown-body input {
font: inherit;
margin: 0;
overflow: visible;
font-family: inherit;
font-size: inherit;
line-height: inherit;
}
.markdown-body [type=button],
.markdown-body [type=reset],
.markdown-body [type=submit] {
-webkit-appearance: button;
appearance: button;
}
.markdown-body [type=checkbox],
.markdown-body [type=radio] {
box-sizing: border-box;
padding: 0;
}
.markdown-body [type=number]::-webkit-inner-spin-button,
.markdown-body [type=number]::-webkit-outer-spin-button {
height: auto;
}
.markdown-body [type=search]::-webkit-search-cancel-button,
.markdown-body [type=search]::-webkit-search-decoration {
-webkit-appearance: none;
appearance: none;
}
.markdown-body ::-webkit-input-placeholder {
color: inherit;
opacity: .54;
}
.markdown-body ::-webkit-file-upload-button {
-webkit-appearance: button;
appearance: button;
font: inherit;
}
.markdown-body a:hover {
text-decoration: underline;
}
.markdown-body ::placeholder {
color: var(--color-fg-subtle);
opacity: 1;
}
.markdown-body hr::before {
display: table;
content: "";
}
.markdown-body hr::after {
display: table;
clear: both;
content: "";
}
.markdown-body table {
border-spacing: 0;
border-collapse: collapse;
display: block;
width: max-content;
max-width: 100%;
overflow: auto;
}
.markdown-body td,
.markdown-body th {
padding: 0;
}
.markdown-body details summary {
cursor: pointer;
}
.markdown-body details:not([open])>*:not(summary) {
display: none !important;
}
.markdown-body a:focus,
.markdown-body [role=button]:focus,
.markdown-body input[type=radio]:focus,
.markdown-body input[type=checkbox]:focus {
outline: 2px solid var(--color-accent-fg);
outline-offset: -2px;
box-shadow: none;
}
.markdown-body a:focus:not(:focus-visible),
.markdown-body [role=button]:focus:not(:focus-visible),
.markdown-body input[type=radio]:focus:not(:focus-visible),
.markdown-body input[type=checkbox]:focus:not(:focus-visible) {
outline: solid 1px transparent;
}
.markdown-body a:focus-visible,
.markdown-body [role=button]:focus-visible,
.markdown-body input[type=radio]:focus-visible,
.markdown-body input[type=checkbox]:focus-visible {
outline: 2px solid var(--color-accent-fg);
outline-offset: -2px;
box-shadow: none;
}
.markdown-body a:not([class]):focus,
.markdown-body a:not([class]):focus-visible,
.markdown-body input[type=radio]:focus,
.markdown-body input[type=radio]:focus-visible,
.markdown-body input[type=checkbox]:focus,
.markdown-body input[type=checkbox]:focus-visible {
outline-offset: 0;
}
.markdown-body kbd {
display: inline-block;
padding: 3px 5px;
font: 11px ui-monospace,SFMono-Regular,SF Mono,Menlo,Consolas,Liberation Mono,monospace;
line-height: 10px;
color: var(--color-fg-default);
vertical-align: middle;
background-color: var(--color-canvas-subtle);
border: solid 1px var(--color-neutral-muted);
border-bottom-color: var(--color-neutral-muted);
border-radius: 6px;
box-shadow: inset 0 -1px 0 var(--color-neutral-muted);
}
.markdown-body h1,
.markdown-body h2,
.markdown-body h3,
.markdown-body h4,
.markdown-body h5,
.markdown-body h6 {
margin-top: 24px;
margin-bottom: 16px;
font-weight: var(--base-text-weight-semibold, 600);
line-height: 1.25;
}
.markdown-body h2 {
font-weight: var(--base-text-weight-semibold, 600);
padding-bottom: .3em;
font-size: 1.5em;
border-bottom: 1px solid var(--color-border-muted);
}
.markdown-body h3 {
font-weight: var(--base-text-weight-semibold, 600);
font-size: 1.25em;
}
.markdown-body h4 {
font-weight: var(--base-text-weight-semibold, 600);
font-size: 1em;
}
.markdown-body h5 {
font-weight: var(--base-text-weight-semibold, 600);
font-size: .875em;
}
.markdown-body h6 {
font-weight: var(--base-text-weight-semibold, 600);
font-size: .85em;
color: var(--color-fg-muted);
}
.markdown-body p {
margin-top: 0;
margin-bottom: 10px;
}
.markdown-body blockquote {
margin: 0;
padding: 0 1em;
color: var(--color-fg-muted);
border-left: .25em solid var(--color-border-default);
}
.markdown-body ul,
.markdown-body ol {
margin-top: 0;
margin-bottom: 0;
padding-left: 2em;
}
.markdown-body ol ol,
.markdown-body ul ol {
list-style-type: lower-roman;
}
.markdown-body ul ul ol,
.markdown-body ul ol ol,
.markdown-body ol ul ol,
.markdown-body ol ol ol {
list-style-type: lower-alpha;
}
.markdown-body dd {
margin-left: 0;
}
.markdown-body tt,
.markdown-body code,
.markdown-body samp {
font-family: ui-monospace,SFMono-Regular,SF Mono,Menlo,Consolas,Liberation Mono,monospace;
font-size: 12px;
}
.markdown-body pre {
margin-top: 0;
margin-bottom: 0;
font-family: ui-monospace,SFMono-Regular,SF Mono,Menlo,Consolas,Liberation Mono,monospace;
font-size: 12px;
word-wrap: normal;
}
.markdown-body .octicon {
display: inline-block;
overflow: visible !important;
vertical-align: text-bottom;
fill: currentColor;
}
.markdown-body input::-webkit-outer-spin-button,
.markdown-body input::-webkit-inner-spin-button {
margin: 0;
-webkit-appearance: none;
appearance: none;
}
.markdown-body .mr-2 {
margin-right: var(--base-size-8, 8px) !important;
}
.markdown-body::before {
display: table;
content: "";
}
.markdown-body::after {
display: table;
clear: both;
content: "";
}
.markdown-body>*:first-child {
margin-top: 0 !important;
}
.markdown-body>*:last-child {
margin-bottom: 0 !important;
}
.markdown-body a:not([href]) {
color: inherit;
text-decoration: none;
}
.markdown-body .absent {
color: var(--color-danger-fg);
}
.markdown-body .anchor {
float: left;
padding-right: 4px;
margin-left: -20px;
line-height: 1;
}
.markdown-body .anchor:focus {
outline: none;
}
.markdown-body p,
.markdown-body blockquote,
.markdown-body ul,
.markdown-body ol,
.markdown-body dl,
.markdown-body table,
.markdown-body pre,
.markdown-body details {
margin-top: 0;
margin-bottom: 16px;
}
.markdown-body blockquote>:first-child {
margin-top: 0;
}
.markdown-body blockquote>:last-child {
margin-bottom: 0;
}
.markdown-body h1 .octicon-link,
.markdown-body h2 .octicon-link,
.markdown-body h3 .octicon-link,
.markdown-body h4 .octicon-link,
.markdown-body h5 .octicon-link,
.markdown-body h6 .octicon-link {
color: var(--color-fg-default);
vertical-align: middle;
visibility: hidden;
}
.markdown-body h1:hover .anchor,
.markdown-body h2:hover .anchor,
.markdown-body h3:hover .anchor,
.markdown-body h4:hover .anchor,
.markdown-body h5:hover .anchor,
.markdown-body h6:hover .anchor {
text-decoration: none;
}
.markdown-body h1:hover .anchor .octicon-link,
.markdown-body h2:hover .anchor .octicon-link,
.markdown-body h3:hover .anchor .octicon-link,
.markdown-body h4:hover .anchor .octicon-link,
.markdown-body h5:hover .anchor .octicon-link,
.markdown-body h6:hover .anchor .octicon-link {
visibility: visible;
}
.markdown-body h1 tt,
.markdown-body h1 code,
.markdown-body h2 tt,
.markdown-body h2 code,
.markdown-body h3 tt,
.markdown-body h3 code,
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</style><title>delete-i</title></head><body><article class="markdown-body"><pre><code>Proposal for C2y
WG14 3786
Title: Remove the imaginary I, v2
Author, affiliation: Alex Celeste, Perforce
Date: 2026-01-12
Proposal category: Feature removal
Target audience: Library implementers, users
</code></pre>
<div class="markdown-heading"><h2 class="heading-element">Abstract</h2><a id="user-content-abstract" class="anchor" aria-label="Permalink: Abstract" href="#abstract"><span aria-hidden="true" class="octicon octicon-link"></span></a></div>
<p>The enforced definition of <code>I</code> frequently obstructs the intent of the user,
replacing identifiers intended to declare other entities with a syntax error.
Audience feedback suggests that this is more common than intentional use of
the feature, so the feature should be removed.</p>
<p>As of Fall 2024, a macro is no longer required, as C2Y provides a true literal.</p>
<hr>
<div class="markdown-heading"><h1 class="heading-element">Remove the imaginary I, v2</h1><a id="user-content-remove-the-imaginary-i-v2" class="anchor" aria-label="Permalink: Remove the imaginary I, v2" href="#remove-the-imaginary-i-v2"><span aria-hidden="true" class="octicon octicon-link"></span></a></div>
<pre><code>Reply-to: Alex Celeste (aceleste@perforce.com)
Document No: N3786
Revises: N3581
Date: 2025-01-12
</code></pre>
<div class="markdown-heading"><h2 class="heading-element">Summary of Changes</h2><a id="user-content-summary-of-changes" class="anchor" aria-label="Permalink: Summary of Changes" href="#summary-of-changes"><span aria-hidden="true" class="octicon octicon-link"></span></a></div>
<div class="markdown-heading"><h3 class="heading-element">N3786</h3><a id="user-content-n3786" class="anchor" aria-label="Permalink: N3786" href="#n3786"><span aria-hidden="true" class="octicon octicon-link"></span></a></div>
<ul>
<li>additional Committee feedback
<ul>
<li>the name <code>j</code> is not a suitable substitute for the name <code>i</code>
</li>
<li>CFP request to include the NOTE with user definition of <code>I</code>
</li>
</ul>
</li>
<li>rebase on latest working draft
<ul>
<li>remove changes to <code>cproj</code> and Annex G, already fixed by <a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3536.pdf" rel="nofollow">N3536</a> and <a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3537.pdf" rel="nofollow">N3537</a>
</li>
</ul>
</li>
</ul>
<div class="markdown-heading"><h3 class="heading-element">N3581</h3><a id="user-content-n3581" class="anchor" aria-label="Permalink: N3581" href="#n3581"><span aria-hidden="true" class="octicon octicon-link"></span></a></div>
<ul>
<li>finalized with Committee feedback, recommending delete outright without replacement</li>
<li>rebase on latest working draft</li>
</ul>
<div class="markdown-heading"><h3 class="heading-element">N3390</h3><a id="user-content-n3390" class="anchor" aria-label="Permalink: N3390" href="#n3390"><span aria-hidden="true" class="octicon octicon-link"></span></a></div>
<ul>
<li>original proposal</li>
</ul>
<div class="markdown-heading"><h2 class="heading-element">Introduction</h2><a id="user-content-introduction" class="anchor" aria-label="Permalink: Introduction" href="#introduction"><span aria-hidden="true" class="octicon octicon-link"></span></a></div>
<p>During the discussion of <a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3274.pdf" rel="nofollow">N3274</a> and its predecessors, a comment was raised
in WG14 session that the macro <code>I</code> was a frequent source of nuisance to both C
and C++ programmers.</p>
<p>For example, in C:</p>
<pre><code>// (from the root file)
#include <complex.h>
// (potentially in another header, not intending to use complex)
enum {
A, B, C, D,
E, F, G, H,
I, J, K, L, // whoops syntax error
};
</code></pre>
<p>or in C++:</p>
<pre><code>template <typename I> // really weird syntax error
void with_range (I begin, I end) {
...
}
</code></pre>
<p>and so on. Because the name is a macro, scope is no help in preventing the error
(except the limited "scope" of a macro parameter, which is not symmetric with the
common use of single-letter names in C++ templates).</p>
<p>Anecdotally, it seems that in usage, this kind of error is at least as common as
intentional use of the feature (obviously it does not generally persist into saved
projects). Reserving a single-letter name is surprising and unreasonable,
especially through a macro.</p>
<p>C2Y introduced genuine literals for complex numbers in <a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3298.htm" rel="nofollow">N3298</a>, while C++ has
provided the literals as a library feature (via the UDL core language functionality)
since <a href="https://isocpp.org/files/papers/N3779.pdf" rel="nofollow">N3779</a> added them to C++14. Therefore, in both languages it is now possible
to write:</p>
<pre><code>auto cf = 1.0i;
</code></pre>
<p>declaring <code>cf</code> as an object of type <code>_Complex double</code> or <code>std::complex <double></code>,
without needing to write</p>
<pre><code>auto cf = 1.0 * I;
</code></pre>
<p>(which could potentially even have a different type since the type of <code>I</code> is
implementation defined)</p>
<p>In the presence of the new features the standard macro is therefore redundant.
As a feature test, <code>_Complex_I</code> would remain available and makes more sense to use
in that way.</p>
<p>At the Spring 2025 meeting the Committee expressed a preference to delete the
macro without a <code>constexpr</code> replacement, as it is easy for the user to define
for themselves.</p>
<div class="markdown-heading"><h2 class="heading-element">Alternative</h2><a id="user-content-alternative" class="anchor" aria-label="Permalink: Alternative" href="#alternative"><span aria-hidden="true" class="octicon octicon-link"></span></a></div>
<p>Because C23 added <code>constexpr</code>, an alternative that would allow most arithmetic
uses of <code>I</code> to continue working unchanged might be:</p>
<pre><code>// in complex.h:
constexpr auto I = _Complex_I;
</code></pre>
<p>This would eliminate the surprising syntax errors caused by macro replacement,
although the name itself would still be reserved in the global scope.</p>
<p>Because the underlying definition of <code>I</code> is left to the implementation (and requires
builtin magic or extensions prior to C2Y's introduction of true literals), it
seems unlikely that much code relies on the textual replacement of the <code>I</code> macro
being stable in any particular form.</p>
<p>Optionally, the header could still define</p>
<pre><code>#define I I
</code></pre>
<p>to act as a feature test. Whether this is useful or not is unclear, but it does
not have the same problem as a macro that would expand to expression tokens.</p>
<div class="markdown-heading"><h2 class="heading-element">Impact</h2><a id="user-content-impact" class="anchor" aria-label="Permalink: Impact" href="#impact"><span aria-hidden="true" class="octicon octicon-link"></span></a></div>
<p>Existing user code presumably relies on <code>I</code>.</p>
<p>Library implementations should guard the definition of the macro behind a version
check to continue to provide compatibility with C23 and earlier. This is not
particularly burdensome.</p>
<p>Code that uses <code>I</code> and wants to continue to compile in C2Y can always simply add
the definition explicitly:</p>
<pre><code>#include <complex.h>
#define I _Complex_I
// or
constexpr auto I = _Complex_I;
</code></pre>
<p>Although implementations are generally free to declare more entities in their headers
than just those specified by the Standard, for this proposal to have a useful impact,
the macro should actually be removed rather than left in place anyway. Implementations
should be encouraged to guard it with a version check or WANT flag rather than take
no action and leave the definition present as an extension (which would be conforming,
but not helpful).</p>
<div class="markdown-heading"><h2 class="heading-element">Proposed wording</h2><a id="user-content-proposed-wording" class="anchor" aria-label="Permalink: Proposed wording" href="#proposed-wording"><span aria-hidden="true" class="octicon octicon-link"></span></a></div>
<p>The proposed changes are based on the latest public draft of C2y, which is
<a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3685.pdf" rel="nofollow">N3685</a>. Bolded text is new text when inlined into an existing sentence.</p>
<p>Modify 7.3 "Complex arithmetic <code><complex.h></code>":</p>
<p>Modify paragraph 3, deleting the references to <code>I</code> as a macro:</p>
<blockquote>
<p>The macro <code>complex</code> expands to <code>_Complex</code>; the macro <code>_Complex_I</code> expands to an
arithmetic constant expression of type <code>float _Complex</code> with the value of its real
part being positive or unsigned zero and the value of its imaginary part being one.
Notwithstanding the provisions of 7.1.3</p>
<ul>
<li>a program may undefine and perhaps then redefine the macro <code>complex</code>;</li>
</ul>
<p>...</p>
</blockquote>
<p>Add a new paragraph to 7.3.1 after paragraph 4:</p>
<blockquote>
<p>NOTE Previous editions of this document also provided a constant <code>I</code>, which might
be defined in user code as follows:</p>
<pre><code>#include <complex.h>
#define I _Complex_I
// or
constexpr auto I = _Complex_I;
</code></pre>
</blockquote>
<p>Replace references to <code>I</code> in the rest of the text with <code>1.0fi</code> or equivalent:</p>
<p>Modify 6.7.2 paragraph 21 (example 5), definition of <code>fc3</code>:</p>
<blockquote>
<pre><code>constexpr float _Complex fc3 = 3.0i; // ok
</code></pre>
</blockquote>
<p>(this example is demonstrating that the conversion does not lose value and should
therefore <strong>not</strong> be changed to use <code>3.0fi</code>)</p>
<p>Modify 6.7.11 paragraph 28:</p>
<blockquote>
<p><strong>EXAMPLE 1</strong> Provided that <code><complex.h></code> has been included, the declarations</p>
<pre><code>int n = 3.5;
double complex c = 5 + 3.0i;
</code></pre>
<p>define and initialize <strong><code>n</code></strong> with the value 3 and <code>c</code> with the value <strong>5 + <em>i</em> 3</strong>.</p>
</blockquote>
<p>(Editorial note: this renames the variable <code>i</code> in the example to <code>n</code>, to avoid confusion
with the imaginary unit invoked by the text description of the subsequent line; this also
changes the spelling of the value expression of <code>c</code> to be math, not code, at CFP request)</p>
<div class="markdown-heading"><h2 class="heading-element">Questions for WG14</h2><a id="user-content-questions-for-wg14" class="anchor" aria-label="Permalink: Questions for WG14" href="#questions-for-wg14"><span aria-hidden="true" class="octicon octicon-link"></span></a></div>
<p>Does WG14 want to remove the <code>I</code> macro from <code><complex.h></code> in C2y?</p>
<p>Would WG14 like to replace the <code>I</code> macro with a C declaration of a named constant
<code>I</code> that does not introduce a macro?</p>
<div class="markdown-heading"><h2 class="heading-element">References</h2><a id="user-content-references" class="anchor" aria-label="Permalink: References" href="#references"><span aria-hidden="true" class="octicon octicon-link"></span></a></div>
<p><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3685.pdf" rel="nofollow">C2y public draft</a><br>
<a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3274.pdf" rel="nofollow">N3274 Remove imaginary types, v3</a><br>
<a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3298.htm" rel="nofollow">N3298 Introduce complex literals, v2</a><br>
<a href="https://isocpp.org/files/papers/N3779.pdf" rel="nofollow">N3779 User-defined literals for std::complex</a><br>
<a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3536.pdf" rel="nofollow">N3536 Clarify wording for 7.3.9.5 - cproj</a><br>
<a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3537.pdf" rel="nofollow">N3537 Correct and clarify 7.3.1 Introduction of Complex arithmetic</a></p>
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